retinoscopy

Question 1

what are the refractive states of the eye?

Answer 1

. emmetropia
. myopia
. hyperopia

Question 2

what is emmetropia ?

Answer 2

. a distant object is in sharp focus on the retina with the lens of eye in a relaxed state

Question 3

what is myopia?

Answer 3

. focused in front of the retina

Question 4

what is hyperopia?

Answer 4

. focused behind retina

Question 5

how do we get light to focus on retina ?

Answer 5

by using lenses this process is called refraction

Question 6

what are the two types of refraction ?

Answer 6

. objective - retinoscopy ( using lenses )

. subjective - using lenses

Question 7

what is retinoscopy?

Answer 7

an objective technique to determine the refractive error of the eye

Question 8

what are the advantage of using retinoscopy?

Answer 8

. quick
. easy
. reliable
. requires minimal co-operation from the patient

Question 9

how does retinoscopy work?

Answer 9

. light is shone into the eye through the pupil
. optometrists sweeps the retinoscope from side to side
and observes movement of reflex compared to the beam
. the reflection tell us if our light is focused on fundus or not

Question 10

what is beam?

Answer 10

light reflected from the anterior eye

Question 11

what is reflex?

Answer 11

light reflected from fundus (back of eye )

Question 12

what is a spot retinoscope?

Answer 12

. spot allows you to see both principle meridians at same time
. easier for children

Question 13

what is a streak retinoscope?

Answer 13

. better at detecting and correcting small amounts of astigmatism
. axis easier to determine more accurately , especially in high CYL

Question 14

how to set up a retinoscope?

Answer 14

. set up at same visual axis - eye level

Question 15

what is working distance ?

Answer 15

distance from retinoscope to patients eye

Question 16

what distance is retinoscope usually held at ?

Answer 16

. 2/3 m = 66cm from the eye arm lenght

Question 17

what is the implication of working distance ?

Answer 17

. we use retinoscopy to find refractive correction needed for the eye when looking at a distant object
. however our retinoscope light is short distance from eye
.need to be close distance
. light from a source that is close to the eye is divergent and will be focused further back
. this means that eye will seem to be more long-sighted than it is
. retinoscopy result correct divergence and gives us more positive result
we must remove extra positive power (give person more plus power than it actually needs) which is not needed when viewing object far away.
-This is where the arm distance comes in
-If we know how far from our eyes patient we are working from you can find out the divergence of light from the eye.

Question 18

how to remove working distance ?

Answer 18

. so at about 2/3 m our light has divergence of +1.50 DS
. to neutralise divergence we need +1.50 DS lens
. we need to reduce our estimate by +1.50DS

Question 19

what to do if ret beam is horizontal ?

Answer 19

sweep ret vetically

Question 20

what to do if ret beam is vertical?

Answer 20

sweep ret horizontally

Question 21

what does it mean if ret reflex movement is a with ?

Answer 21

indicates eye is hyperopic or has low myopia

Question 22

how to correct with movement ?

Answer 22

add positive lens

Question 23

what does a positive lens do ?

Answer 23

causes convergence of light as it passes through the eye

Question 24

why can a with movement has slight myopia ?

Answer 24

due to working distance

Question 25

what does an against movement indicate ?

Answer 25

myopia

Question 26

what type of lens should you use to correct myopia?

Answer 26

negative lens

Question 27

what does dull and slow movement mean ?

Answer 27

large refractive error

add high power lens

Question 28

what does bright and fast mean?

Answer 28

small refractive error

add low power lens

Question 29

what does bright and no movement mean ?

Answer 29

no lens required

you have reached reversal

Question 30

how do you know when you have reached reversal ?

Answer 30

no movement and whole pupil reflects light as beam is moved

Question 31

how to improve accuracy in you ret?

Answer 31

-wear your own specs or CL so no error made for patient
-ensure working distance remains constant: check this by checking you are at arms distance
-limit number of sweeps
make quick decisions

Question 32

How do we know whether light is focused in the right place?

Answer 32

• Ask patient what they can see

- Ask to read out

Question 33

what is astigmatism ?

Answer 33

. a visual defect in which the unequal curvature of one or more refractive surfaces of the eye prevents light rays from focusing clearly at one point on retina
. there are two focal points each formed by one of the two different curvatures of the cornea or lens
. these 2 curvatures are almost always perpendicular to each other

Question 34

how many meridians are there in astigmatic eye ?

Answer 34

steep meridian = more curved

flat meridian = less curved

Question 35

how to correct spherical ametropia ?

Answer 35

. one power in all meridia

. need only one spherical lens

Question 36

how to correct astigmatic ametropia ?

Answer 36

. different powers in the 2 principal meridia
. use spherical and cylindrical lenses
we then have the power of sphere only in one meridian and the power of the sphere plus cylinder in the perpendicular meridian
. NB: principal meridia almost always 90deg to each other

Question 37

how to visualise a cylinder ?

Answer 37

think of a cylindrical object such as glass with curvature in one meridian and in the perpendicular meridian there is no power